US Dept. of Energy, Project Partners Aim to Drive Down Cost of Solar Thermal Desalination

The US Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE) Solar Technologies Office (STO) on June 19 announced USD21 million of funding for new projects aimed at advancing solar-thermal desalination and water treatment technologies. Later that same week, EERE , on behalf of its Advanced Manufacturing Office, announced it would issue a Funding Opportunity Announcement (FOA) that would see creation of an Energy-Water Desalination Hub.

The Solar Desalination funding program. | Credit: US Dept. of Energy

Desalination treats seawater, brackish water and contaminated water so that it can be used in municipal, industrial and agricultural water supplies, or to serve other water reclamation needs, the agency explains. Most desalination operations are grid-connected, which limits their use to facilities with grid access. Making use of thermal energy produced by concentrating solar power (CSP) technology would enable off-grid and smaller scale desalination systems to be deployed, thereby expanding opportunities substantially.

The 14 solar-thermal water desalination R&D projects, anticipated to last up to three years, aim to reduce the cost of solar-thermal desalination and apply solar-thermal technologies in new, innovative, off-grid industry and market sectors.

STO has identified four markets it believes are particularly attractive for solar desalination: municipal water production, agriculture, industrial processes, and the purification of water produced from energy development – oil and gas extraction in particular.

Funding for early-stage, long-term solar desalination R&D

More specifically, STO and solar-thermal desalination R&D awardees aim to drive the cost of small-scale plants that process low volumes of high-salinity water, such as brine from oil and gas operations, down to a levelized cost of water (LCOW) of USD1.50 per cubic meter. The corresponding LCOW target for large-scale plants that process high volumes of low-salinity water, such as seawater for a municipal utility, is USD0.50 per cubic meter.

The DOE-EERE-STO funding comes in the form of cooperative agreements, which require the awardees to invest from 20-50 percent of estimated total project costs. That helps assure the highest possible rate of return on investment for the taxpayer funds invested. Some USD30 million in public-private funds will be invested in the 14 solar desalination R&D projects in total, according to the agency.

The projects the agency is funding involve early-stage, long-term R&D technologies, Solar Desalination Acting Program Manager Avi Schultz explained in an interview. That said, the agency believes that using solar thermal energy produced by CSP rather than electricity will eventually result in increasing the energy efficiency of water treatment processes or lowering capital investment costs in the case of reverse osmosis for desalination.

The most common means of desalination is reverse osmosis, which entails using electrical power to pressurize and pump untreated water through a membrane filter to remove contaminants. Despite advances, it remains a relatively expensive source of freshwater, Shultz noted.

“We do see opportunities, and the reason we got involved in this program is that we see a growing need for freshwater and water treatment technologies for municipal and agricultural markets, and nearer term to use CSP thermal energy for treatment of highly saline waters produced by oil and gas exploration and extraction,” Schultz told Solar Magazine.

The Solar Desalination funding program aims to address four topic areas. Click here to view the full-size graphics. | Credit: US Dept. of Energy

“Obviously, thermal energy produced by CSP is a less refined form of energy than electricity, a highly refined form of energy,” he said. That means less effort needs to be expended to collect, store and use it.

That, in turn, translates into lower costs. Producing clean, safe freshwater via current, “state of the art” reverse osmosis in the US costs about USD1.50 per cubic meter, according to EERE-STO. The agency and solar-thermal R&D project partners aim to reduce that to USD0.50 per cubic meter.

“Replacing electrical energy input with solar thermal energy may be cheaper, even though it’s not as efficient as a form of energy,” Schultz said. “We believe that if we hit our target, solar-desalinated water becomes cost-competitive with other sources of freshwater in the US.”

EERE-STO and project R&D awardees can build and deploy modular, smaller scale solar-thermal desalination and water treatment systems by making use of thermal as opposed to electrical energy. That’s one of the key, distinguishing aspects of the technologies they’re aiming to develop, Schultz explained.

“These types of plants are really driven by two things: the need to generate high temperatures and gain a lot in terms of process efficiency – a solar power tower-type CSP design, for example,” Schultz said. Secondly, the ability to scale down CSP systems is limited as a result of the need to produce sufficient energy to fuel a steam-turbine generator.

The smallest conventional CSP electricity facilities are about 100 megawatts (MW) as a result. “That’s not true for direct solar-thermal desalination, which potentially can be scaled down to 10 MW, even 1 MW or less. And we don’t lose that efficiency going down to that small scale,” Schultz said.

Furthermore, energy-efficiency losses can be avoided by making use of solar-thermal energy from a CSP system for desalination as opposed to using it to fuel a generator. “You don’t need the high temperatures…and you don’t have the energy losses, which are unique to steam-turbine generators, but not to desalination,” Schultz said.

CSP solar towers need to generate enough heat to raise process temperatures up to around 565 degrees Celsius, according to Schultz. Depending on the type of application, temperatures associated with the solar-thermal desalination technologies EERE-STO is funding only range from about 50 degrees Celsius to about 200 degrees Celsius.

Near and long-term solar desalination goals and applications

Producing potable, drinking water USD0.50 per cubic meter is a longer term goal of the solar-thermal desalination program. Nearer term, EERE-STO sees opportunities to process and treat highly saline water from oil and gas extraction and other, smaller scale, distributed operations.

“Desalination of oil and gas brine is probably one of the first applications for this technology. The industry is dealing with higher costs now and they don’t have a really good technology for dealing with it at present,” Schultz said.

More generally, EERE-STO is targeting a solar-thermal desalination cost of around USD1.50 per cubic meter for smaller scale, highly saline water treatment applications. “We can move away from having to use electricity and rely on thermal energy to pump freshwater through system processes. Some awardees eliminate that [use of electricity] entirely,” Schultz pointed out.

Schultz said that it’s difficult to say when any one or more of the solar-thermal desalination technologies the agency is funding might be commercialized. “One of the tricky things about water treatment is that every water resource is different. It’s valuable to have a suite of tools and methods ready at hand.”

Venturing an estimate, “I would say five years would be the shortest possible time frame, but it may be possibly 10 years before one of these technologies is ready to be picked up by industry,” Schultz said.

Along the same lines as the solar-thermal desalination R&D program, EERE’s proposed Energy-Water Desalination Hub would accelerate technological advances and lower the cost of solar-thermal desalination to produce clean, safe drinking water. Plans entail creation of multiple, collaborative science and engineering R&D teams, as well as economic and public policy disciplines where appropriate. As envisaged, these will span industry, academia, DOE’s network of national laboratories and other stakeholders, according to a news release.

The Energy-Water Desalination Hub would take a cohesive approach in creating a strategic portfolio of technologies deemed to have the greatest potential impact regarding energy efficiency, water efficiency and cost reductions so as to achieve so-called “pipe parity” of desalinated freshwater from a range of water sources, EERE explains.

EERE anticipates the hub will focus on four, key technical areas of interest: materials R&D, new processes R&D, modeling and simulation tools and integrated data and analysis. The agency expects to issue the FOA this month (July).

Solar thermal energy and agriculture

Using solar-thermal energy for desalination and treatment of water used in agriculture is another focal point of the EERE-STO R&D program. “One of the challenges is the cost structure,” Schultz said. “The first markets to adopt new technologies are typically the ones facing higher costs and the ability to pay for water purification. That’s primarily industrial wastewater, as well as oil and gas producers.”

In contrast, profit margins are inherently low for agricultural commodity producers. “We don’t necessarily expect agriculture to be one of the first markets to deploy solar-thermal desalination, but one of the advantages of the technologies we’re developing is that they can be small scale and distributed. It’s certainly a sector and market we’re looking into and interested in developing,” Schultz said.

Among the 14 solar desalination projects, EERE-STO awarded Livermore, California-based Sunvapor USD1.5 million of cooperative funding to carry out a “Solar Steam on Demand” R&D project. Sunvapor will invest USD1 million of capital in the project, which aims to apply its CSP technology as a source of heat energy capable of producing steam at a temperature of around 180 degrees Celsius (356 degrees Fahrenheit).

Sunvapor will also develop a thermal energy storage solution based on phase-change materials, which will capture heat from producing steam and store it in phase-change materials that change from liquid to solid and vice-versa. This will be combined with the company’s solar collector, a highly efficient, low-cost CSP technology Sunvapor developed in part with USD2.2 million of previous funding from DOE’s SunShot Initiative.

Sunvapor expects the solar-thermal water purification-distillation system, dubbed “Solar Steam on Demand,” will be able to operate continuously, night and day, at a levelized cost of heat of USD0.015 per kilowatt-hour. That would meet the requirements of agricultural and industrial heating applications, according to EERE-STO and the company.

This award will help us demonstrate that the cost of solar can be drastically cut by taking advantage of renewable fiber-reinforced composite materials.

– Sunvapor CEO Philip Gleckman said upon announcement of the DOE SunShot award in July 2016. “Our digitally optimized designs look different and have a simpler construction because we are liberated from the rules that apply to steel.”

The “Sleeping Giant of Renewable Energy”

Fuel for process heat accounts for nearly half of all the primary energy used by manufacturers in the USA and makes up one-fifth national greenhouse gas emissions, Sunvapor pointed out at the time. “Solar process steam is the Sleeping Giant of renewable energy,” said James Valenti-Jordan, a Sunvapor advisor who formerly worked for the Campbell Soup Company. “Sunvapor’s breakthrough collector will enable food processors to purchase steam at lower prices than natural gas,” he was quoted in the news release.

Thermo-compression (or re-compression) and vapor-absorption heat pumps are the two technologies used to treat and process water in industrial applications. Both require temperatures around 180 degrees Celsius, according to Gleckman. “The issue is that there hasn’t been a cost-effective solar solution to efficiently distill water and generate steam as yet. What we’ve shown in our earlier, SunShot program project is a path to low-cost steam generation using CSP,” Gleckman explained in an interview.

An initial, 50-kilowatt (kW) pilot-demonstration instance of Sunvapor’s “Solar Steam on Demand” system – excluding energy storage – is up and running at grower-owned and operated Horizon Nut as a result of Sunvapor’s SunShot award. It’s being used to distill water and produce steam to dry pistachios, which Horizon Nut stores in silos that can contain as much as 1 million pounds of pistachios each. “To our knowledge it’s the first permitted solar-nut dryer in the country, but certainly in Fresno County, California,” Gleckman said.

Horizon Nut pistachio trees.

Sunvapor’s CSP technology transforms solar energy into heat that can be used for all of the food industry’s needs at a cost competitive with natural gas. These can range from steam pasteurization, to drying, blanching, cleaning, and roasting, according to the news release.

Food processors in California consume more than 11-terrawatt-hours (TWh) of energy per year – the equivalent of burning 300 million gallons of gasoline annually, Sunvapor points out. Substituting CSP for natural gas would also reduce carbon emissions significantly – the equivalent of taking half a million cars off the road, according to the company.

Sunvapor intends to build upon its success at Horizon Nut by incorporating thermal energy storage into its “Solar Steam on Demand” system so that distillation equipment or an evaporator could be used after the sun sets. “It’s a platform that could be used for desalination, but in most cases to produce steam heat for industrial processes,” Gleckman told Solar Magazine.

There are really two areas of innovation here: one is a structural design that gets us to low-cost installations. The second is a low-cost, solar-steam energy storage system.

Sunvapor expects to be able to achieve an installed system cost for solar-steam energy storage of USD50 per square meter. “We don’t really see any technology competing with our approach. Basically, we use the lowest cost, structural materials and we have a high-performance, overall system design,” Gleckman said.

“This is exactly the kind of breakthrough we need: technology, once it is mature, that can stand on its own without government subsidies. The opportunity to build a solar steam economy in the region has the potential to create thousands of good jobs and improve the air quality,” said California State Assemblyman and vice-chair of the Utilities and Energy Committee Jim Patterson.

EERE-STO’s latest awards focus on desalination, but the agency sees lots of opportunities when it comes to using CSP thermal energy to fuel a wide range of industrial processes. “We see these awards as a first step into this space. Up until recently we’ve been focused on electricity, so it should be very interesting to see the results and how this all works out,” Shultz concluded. comment

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